一个用矩形法求定积分的通用程序。编译，连接均无问题，但运行结果为：floating point divided by 0.

程序如下： #include<math.h> #define E 1e-8 main() { double integral(float low,float up,double (*fun)()); double i_value; printf("\nThe integral of sin(x) from 0 to 1 is:\n"); i_value=integral(0,1,sin); printf("%.8f\n",i_value); printf("The integral of cos(x) from -1 to 1 is:\n"); i_value=integral(-1,1,cos); printf("%.8f\n",i_value); printf("The integral of exp(x) from 0 to 2 is:\n"); printf("%.8f\n",i_value); }

double integral(float low,float up,double (*fun)()) { double h,sum=0,intg1,intg2=0; int i,n=10; h=(up-low)/n; for(i=0;i<n;i++) sum+=(*fun)(low+i*h); intg1=sum*h; for(;fabs(intg2-intg1)>E;) { n*=2; h=(up-low)/n; for(sum=0,i=0;i<n;i++) sum+=(*fun)(low+i*h); intg2=sum*h; } return intg2; }

不好意思，刚才的程序中有明显的低级错误，如：主函数中漏掉了语句{i_value=integral(0,2,exp);},函数integral的形参表中(*fun)后的括号中漏掉了double x(这是一棵芦苇兄找出的错误）。但做了改正后的程序仍然出现同样的运行结果：

The integral of sin(x) from 0 to 1 is:

Floating point error:Davide by 0

改正后的程序如下：

#include<math.h> #define E 1e-8 main() { double integral(float low,float up,double (*fun)(double x)); double i_value;

printf("\nThe integral of sin(x) from 0 to 1 is:\n"); i_value=integral(0,1,sin); printf("%.8f\n",i_value);

printf("The integral of cos(x) from -1 to 1 is:\n"); i_value=integral(-1,1,cos); printf("%.8f\n",i_value);

printf("The integral of exp(x) from 0 to 2 is:\n"); i_value=integral(0,2,exp); printf("%.8f\n",i_value); }

double integral(float low,float up,double (*fun)(double x)) { double h,sum=0,intg1,intg2=0; int i,n=10; /*先求一个初始值*/

h=(up-low)/n; /*h为步长*/ for(i=0;i<n;i++) sum+=(*fun)(low+i*h); intg1=sum*h; /*若相邻两次的积分值绝对值之差不超过所设精度E，就结束循环*/

for(;fabs(intg2-intg1)>E;) { n*=2; h=(up-low)/n; for(sum=0,i=0;i<n;i++) sum+=(*fun)(low+i*h); intg2=sum*h; } return intg2; }